Aquatic habitats are increasingly exposed to chemicals that, even at low levels, can disturb the endocrinology of organisms. These endocrine disrupting chemicals (EDCs) can have severe impacts on reproductive physiology, yet knowledge of their effects on evolutionary processes and population viability is fundamentally lacking. Using the invasive mosquitofish Gambusia holbrooki, the Fellow will use behavioural and genetic assays to reveal how EDCs impact reproductive success and sexual selection. This study will be the first to examine the effects of EDCs on both female and male reproductive behaviour and quality of offspring. Crucially, in a novel approach, cutting-edge, Next Generation Sequencing (NGS) will be used to explore EDC-induced changes in gene expression in the Central Nervous System. The Fellow will expose mosquitofish to 17α-ethynyl estradiol (EE2), a synthetic estrogen used in oral contraceptive pills, and experimentally determine how exposure affects fish reproductive behaviour, reproductive success and gene expression. The Fellow will establish transcriptomic profiles of the fish brain, ovary or testis with NGS and use digital transcriptomics to analyse the effects of EE2 exposure on gene expression. The identity and extent of change of the differentially expressed transcripts will be interpreted with respect to the observed behavioural changes. This study will deepen our knowledge on the genetics of how organisms adapt to human-induced environmental changes and provide evidence on how genome and environment interact.The joint programme of research and training will allow the Fellow to use her existing expertise in behavioural ecotoxicology and critically to engage with new techniques. The programme will give the Fellow competencies in research-related activities and state-of-the-art NGS and bioinformatics that are essential to her in becoming an independent scientist able to command her own research funding and supervise a research team.